Annular premixed pilot in fuel nozzle

ABSTRACT

A combustor for a gas turbine engine has a head end portion that carries at least one fuel/air nozzle. Each fuel/air nozzle includes a premixed pilot nozzle having premix conduits that are configured with concentric axes that direct the fuel/air mixture axially from the premixed pilot nozzle. The premixed pilot nozzle can include an annular channel disposed radially outwardly from the premix and including air jets that direct air radially outwardly from the premix conduits.

FIELD OF THE INVENTION

The present invention generally involves a gas turbine engine that combusts a hydrocarbon fuel mixed with air to generate a high temperature gas stream that drives turbine blades to rotate a shaft attached to the blades and more particularly to the engine's fuel nozzle having a pilot nozzle that premixes fuel and air while achieving lower nitrogen oxides.

BACKGROUND OF THE INVENTION

Gas turbine engines are widely used to generate power for numerous applications. A conventional gas turbine engine includes a compressor, a combustor, and a turbine. In a typical gas turbine engine, the compressor provides compressed air to the combustor. The air entering the combustor is mixed with fuel and combusted. Hot gases of combustion are exhausted from the combustor and flow into the blades of the turbine so as to rotate the shaft of the turbine connected to the blades. Some of that mechanical energy of the rotating shaft drives the compressor and/or other mechanical systems.

As government regulations disfavor the release of nitrogen oxides into the atmosphere, their production as byproducts of the operation of gas turbine engines is sought to be maintained below permissible levels. One approach to meeting such regulations is to move from diffusion flame combustors to combustors that employ lean fuel and air mixtures using a fully premixed operations mode to reduce emissions of, for example, nitrogen oxides (commonly denoted NOx) and carbon monoxide (CO). These combustors are variously known in the art as Dry Low NOx (DLN), Dry Low Emissions (DLE) or Lean Pre Mixed (LPM) combustion systems.

Fuel-air mixing affects both the levels of nitrogen oxides generated in the hot gases of combustion of a gas turbine engine and the engine's performance. A gas turbine engine may employ one or more fuel nozzles to intake air and fuel to facilitate fuel/air mixing in the combustor. The fuel nozzles may be located in a head end portion of the combustor, and may be configured to intake an air flow to be mixed with a fuel input. Typically, each fuel nozzle may be internally supported by a center body located inside of the fuel nozzle, and a pilot can be mounted at the downstream end of the center body. As described for example in U.S. Pat. No. 6,438,961, which is incorporated in its entirety herein by this reference for all purposes, a so-called swozzle can be mounted to the exterior of the center body and located upstream from the pilot. The swozzle has curved vanes that extend radially from the center body across an annular flow passage and from which fuel is introduced into the annular flow passage to be entrained into a flow of air that is swirled by the vanes of the swozzle.

Various parameters describing the combustion process in the gas turbine engine correlate with the generation of nitrogen oxides. For example, higher gas temperatures in the combustion reaction zone are responsible for generating higher amounts of nitrogen oxides. One way of lowering these temperatures is by premixing the fuel air mixture and reducing the ratio of fuel to air that is combusted. As the ratio of fuel to air that is combusted is lowered, so too the amount of nitrogen oxides is lowered. However, there is a trade-off in performance of the gas turbine engine. For as the ratio of fuel to air that is combusted is lowered, there is an increased tendency of the flame of the fuel nozzle to blow out and thus render unstable the operation of the gas turbine engine. A pilot of a diffusion flame type has been used for better flame stabilization in a combustor, but doing so increases NOx.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In theory, the closer one comes to having at every point in the combustion chamber, a stoichiometric relationship between the fuel and air that undergoes combustion at a given temperature of combustion, the closer one comes to minimizing the generation of nitrogen oxides as byproducts of the combustion. With a fuel nozzle configured as described below, it becomes possible to achieve a more uniform equivalence ratio across the plane of the center body tip of the outer nozzle and thus more closely approximate achieving in the combustion chamber of the gas turbine engine such theoretical conditions of the desired stoichiometric relationship between the fuel and air that undergoes combustion at a given temperature of combustion. Moreover, to overcome one of the drawbacks of a diffusion flame type of pilot, a premix pilot also can be used as a pilot to stabilize the pilot flame, even in low fuel to air ratio to prevent an increase in NOx.

In one embodiment of the fuel nozzle that includes premix conduits that are configured with concentric axes that are parallel to the burner tube axis to direct the fuel/air mixture axially from the premixed pilot nozzle, there is at least one air jet beside each of the premix conduits wherein each of the air jets is directed radially outwardly from the premix conduits so that each of the air jets can entrain some portion of fuel/air mixture to direct the mixture radially outward from the premix conduits to form a more uniform fuel/air mixture in the burn exit plane of the nozzle and into the combustion chamber of a gas turbine. The air jets desirably are disposed at the downstream end of an annular channel that is disposed radially outwardly of the premix conduits.

In another embodiment of the present invention, each of the premix conduits is itself configured concentrically about a central longitudinal axis disposed at an acute angle with respect to the axis of burner tube to direct the fuel/air mixture radially outwardly about the axis of burner tube to form a more uniform fuel/air mixture in the burn exit plane of the nozzle and into the combustion chamber of a gas turbine.

In another embodiment of the present invention, each of the premix conduits is itself configured concentrically about a bi-directed central longitudinal axis that has a first leg disposed parallel to the axis of burner tube and a second leg disposed at an acute angle with respect to the axis of burner tube to direct the fuel/air mixture radially outwardly about the axis of burner tube to form a more uniform fuel/air mixture in the burn exit plane of the nozzle and into the combustion chamber of a gas turbine.

In a further embodiment of the fuel nozzle in which each of the premix conduits is itself configured concentrically about a central longitudinal axis disposed at an acute angle with respect to the axis of burner tube to direct the fuel/air mixture radially outwardly about the axis of burner tube, there is at least one air jet beside each of the premix conduits so that each of the air jets can entrain some portion of fuel/air mixture to further direct the mixture radially outwardly from the premix conduits to form a more uniform fuel/air mixture in the burn exit plane of the nozzle and into the combustion chamber of a gas turbine. Moreover, one or more of the air jets desirably is directed radially outwardly from the premix conduits to entrain some portion of fuel/air mixture to further direct the mixture radially outwardly from the premix conduits to form a more uniform fuel/air mixture in the burn exit plane of the nozzle and into the combustion chamber of a gas turbine.

Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

FIG. 1 is a block diagram of a turbine system having a fuel nozzle coupled to a combustor in accordance with an embodiment of the present technique;

FIG. 2 is a cross-sectional view of several portions of a combustor in a gas turbine system of the present disclosure;

FIG. 3 depicts an exemplary embodiment of components of the present invention in a view that is partially in perspective and partially in cross section;

FIG. 4 depicts another exemplary embodiment of components of the present invention in a cross sectional view;

FIG. 5 is a cross sectional view taken along the sight lines designated 5-5 in FIG. 4;

FIG. 6 depicts a further exemplary embodiment of components of the present invention in a cross sectional view;

FIG. 7 depicts yet another exemplary embodiment of components of the present invention in a cross sectional view;

FIG. 8 depicts in cross section an alternative exemplary embodiment of the section circumscribed by the dashed outline designated by the numeral 8 in FIG. 6;

FIG. 9 depicts another exemplary embodiment of components of the present invention in a cross sectional view similar to the view shown in FIG. 4;

FIG. 10 schematically represents embodiments of the methods of the present invention for operating a fuel/air nozzle for a gas turbine engine; and

FIG. 11 schematically represents alternative embodiments of the methods of the present invention for operating a fuel/air nozzle for a gas turbine engine.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of embodiments of the invention.

Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

It is to be understood that the ranges and limits mentioned herein include all sub-ranges located within the prescribed limits, inclusive of the limits themselves unless otherwise stated. For instance, a range from 100 to 200 also includes all possible sub-ranges, examples of which are from 100 to 150, 170 to 190, 153 to 162, 145.3 to 149.6, and 187 to 200. Further, a limit of up to 7 also includes a limit of up to 5, up to 3, and up to 4.5, as well as all sub-ranges within the limit, such as from about 0 to 5, which includes 0 and includes 5 and from 5.2 to 7, which includes 5.2 and includes 7.

Referring to FIG. 1, a simplified drawing of several portions of a gas turbine system 10 is illustrated. The turbine system 10 may use liquid or gas fuel, such as natural gas and/or a hydrogen rich synthetic gas, to run the turbine system 10. As depicted, a plurality of fuel nozzles 12 of the type described more fully below intakes a fuel supply 14, mixes the fuel with air, and distributes the air-fuel mixture into a combustor 16. The air-fuel mixture combusts in a chamber within the combustor 16, thereby creating hot pressurized exhaust gases. The combustor 16 directs the exhaust gases through a turbine 18 toward an exhaust outlet 20. As the exhaust gases pass through the turbine 18, the gases force one or more turbine blades to rotate a shaft 22 along an axis of the system 10. As illustrated, the shaft 22 may be connected to various components of the turbine system 10, including a compressor 24. The compressor 24 also includes blades that may be coupled to the shaft 22. As the shaft 22 rotates, the blades within the compressor 24 also rotate, thereby compressing air from an air intake 26 through the compressor 24 and into the fuel nozzles 12 and/or combustor 16. The shaft 22 also may be connected to a load 28, which may be a vehicle or a stationary load, such as an electrical generator in a power plant or a propeller on an aircraft, for example. As will be understood, the load 28 may include any suitable device capable of being powered by the rotational output of turbine system 10.

FIG. 2 is a simplified drawing of cross sectional views of several portions of the gas turbine system 10 schematically depicted in FIG. 1. As schematically shown in FIG. 2, the turbine system 10 includes one or more fuel/air nozzles 12 located in a head end portion 27 of one or more combustors 16 in the gas turbine engine. Each illustrated fuel nozzle 12 may include multiple fuel nozzles integrated together in a group and/or a standalone fuel nozzle, wherein each illustrated fuel nozzle 12 relies at least substantially or entirely on internal structural support (e.g., load bearing fluid passages). Referring to FIG. 2, the system 10 comprises a compressor section 24 for pressurizing a gas, such as air, flowing into the system 10 via air intake 26. In operation, air enters the turbine system 10 through the air intake 26 and may be pressurized in the compressor 24. It should be understood that while the gas may be referred to herein as air, the gas may be any gas suitable for use in a gas turbine system 10. Pressurized air discharged from the compressor section 24 flows into a combustor section 16, which is generally characterized by a plurality of combustors 16 (only one of which is illustrated in FIGS. 1 and 2) disposed in an annular array about an axis of the system 10. The air entering the combustor section 16 is mixed with fuel and combusted within the combustion chamber 32 of the combustor 16. For example, the fuel nozzles 12 may inject a fuel/air mixture into the combustor 16 in a suitable fuel-air ratio for optimal combustion, emissions, fuel consumption, and power output. The combustion generates hot pressurized exhaust gases, which then flow from each combustor 16 to a turbine section 18 (FIG. 1) to drive the system 10 and generate power. The hot gases drive one or more blades (not shown) within the turbine 18 to rotate the shaft 22 and, thus, the compressor 24 and the load 28. The rotation of the shaft 22 causes blades 30 within the compressor 24 to rotate and draw in and pressurize the air received by the intake 26. It readily should be appreciated, however, that a combustor 16 need not be configured as described above and illustrated herein and in general may have any configuration that permits pressurized air to be mixed with fuel, combusted and transferred to a turbine section 18 of the system 10.

FIGS. 3-9 schematically illustrate various embodiments of fuel/air nozzles 12 in accordance with exemplary embodiments of the present invention. In each of FIGS. 4, 8 and 9 for example, at least each upstream end of each premix conduit 41 defines a central axis 41 d configured and disposed so that the flow of fluid that enters the entrance opening 66 a of each premix conduit 41 is directed parallel to the central axis 36 of the centerbody 52. In each of FIGS. 6 and 7 for example, at least each upstream end of each premix conduit 41 defines a central axis 41 d configured and disposed so that the flow of fluid that enters the entrance opening 66 a of each premix conduit 41 is directed at an acute angle away from the central axis 36 of the centerbody 52 in the range of 0.1 degrees to twenty degrees. As schematically shown in FIG. 3 for example, one embodiment of the fuel/air nozzle 12 includes premix conduits 41 that are configured with concentric axes that are parallel to the burner tube axis 36 to direct the fuel/air mixture axially from the premixed pilot nozzle 40. In the embodiments that are schematically shown in FIGS. 4, 5 and 9, there is at least one air jet 42 beside each of the premix conduits 41 wherein each of the air jets 42 can entrain some portion of fuel/air mixture to direct the mixture radially outwardly from the premix conduits 41 to form a more uniform fuel/air mixture in the burn exit plane 44 of the nozzle 12 and into the combustion chamber 32 of the combustor 16 (FIGS. 1 and 2). In the embodiment depicted in FIGS. 4 and 5, each of the air jets 42 desirably is directed radially outwardly from the premix conduits 41 so that each of the air jets 42 more readily can entrain more of the fuel/air mixture to direct more of the mixture radially outwardly from the premix conduits 41 to form a more uniform fuel/air mixture in the burn exit plane 44 of the nozzle 12 and into the combustion chamber 32 of the combustor 16 (FIGS. 1 and 2).

As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine engine desirably includes an axially elongating peripheral wall 50 defining an outer envelope of the nozzle 12. The peripheral wall 50 of fuel/air nozzle 12 has an outer surface 50 a and an inner surface 50 b facing opposite the outer surface 50 a and defining an axially elongating inner cavity 50 c.

As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine engine desirably includes a hollow, axially elongating centerbody 52 disposed within the inner cavity 50 c of the fuel/air nozzle 12 and defining a central axis 36, which is the same as the central axis of the burner tube. The centerbody 52 is defined by a centerbody wall 52 a that defines an upstream end 52 b and a downstream end 52 c disposed axially opposite the upstream end 52 b. The centerbody wall 52 a is defined by an exterior surface 52 d and an interior surface 52 e facing opposite the exterior surface 52 d. The interior surface 52 d of the centerbody wall 52 a defines an axially elongating interior passage 53 that is disposed concentrically about the central axis 36 of the centerbody 52. A primary air flow channel 51 is defined in the annular space between the inner surface 50 b of the peripheral wall 50 and the exterior surface 52 d of the centerbody wall 52 a.

As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine engine desirably includes an axially elongated, hollow fuel supply line 54 extending axially through the interior passage 53 of the centerbody 52. The fuel supply line 54 has an upstream end 54 a that is disposed at the upstream end 52 b of the centerbody 52 and that is configured for connection to a source of fuel (not shown). The fuel supply line 54 has a downstream end 54 b that is disposed at the downstream end 52 c of the centerbody 52. A secondary air flow channel is defined by an annular space between the interior surface 52 e of the centerbody 52 and the exterior surface of the fuel supply line 54, and that annular space defines the axially elongating interior passage 53 schematically shown in FIG. 3.

As schematically shown in FIG. 3, the primary fuel may be supplied to the combustion chamber 32 of the combustor 16 (FIG. 2) through a plurality of air swirler vanes 56 that are fixed and extend across the flow path of the primary air flow channel 51. These air swirler vanes 56 define a so-called swozzle that extends radially from the exterior surface of centerbody wall 52 a. As schematically shown in FIG. 3, each of the air swirler vanes 56 of the swozzle desirably is provided with internal fuel conduits 57 that terminate in fuel injection ports or holes 58 from which primary fuel (indicated by the arrows designated by the numeral 57 a) flowing from the conduits 57 can be injected into the primary air (indicated by the arrows designated by the numeral 51 a) that flows past the fuel injection ports 58 in the air swirler vanes 56. As primary air flow 51 a is directed against the air swirler vanes 56, a swirling pattern is imparted to the primary air flow 51 a that facilitates the mixing of the primary air flow 51 a with the primary fuel that is ejected from the holes 58 of the air swirler vanes 56 into the passing primary air flow 51 a. The primary air flow 51 a mixed with the primary fuel then may flow into the pre-mixing annulus 51 that is defined between the peripheral wall 50 and the inner centerbody 52, wherein the primary air flow 51 a and the primary fuel continue to mix together prior to entering the combustion chamber 32.

As schematically shown in FIG. 3 for example, a fuel/air nozzle 12 for a gas turbine engine desirably includes a premixed pilot nozzle 40 that has an upstream end 40 a connected to the downstream end 52 c of the centerbody 52. In the embodiment depicted in FIG. 3, the downstream end 52 c of the centerbody 52 and the upstream end 40 a of the premixed pilot nozzle 40 are defined in part by different sections of the metal cylinder that forms the centerbody 52 and the outermost wall that defines the premixed pilot nozzle 40. The premixed pilot nozzle 40 has a downstream end 40 b disposed axially opposite the upstream end 40 a of the premixed pilot nozzle 40.

As schematically shown in FIGS. 3, 4 and 9 for example, the premixed pilot nozzle 40 defines a pilot fuel nozzle 60, which defines an upstream end 60 a and a downstream end 60 b. As schematically shown in FIGS. 4 and 9 for example, the upstream end 60 a of the pilot fuel nozzle 60 is connected in fluid communication with the downstream end 54 b of the fuel supply line 54. The downstream end 60 b of the pilot fuel nozzle 60 defines at least one fuel jet 61 configured in fluid communication with the upstream end 60 a of the pilot fuel nozzle 60. As schematically shown by the arrows designated 62 in FIGS. 4 and 9 for example, fuel 62 entering the pilot fuel nozzle 60 via the downstream end 54 b of the fuel supply line 54 exits the pilot fuel nozzle 60 via a plurality of fuel jets 61 (shown in dashed line in FIG. 5).

As schematically shown in FIGS. 3, 4 and 9 for example, the premixed pilot nozzle 40 further defines an annular-shaped fuel plenum wall 63 disposed radially outwardly from the pilot fuel nozzle 60 and desirably concentrically with respect to the burner tube axis 36 shown in FIG. 3. As schematically shown in FIGS. 3, 4 and 9 for example, the fuel plenum wall 63 defines a fuel plenum 64 between the pilot fuel nozzle 60 and the fuel plenum wall 63. As schematically shown in FIGS. 4 and 9 for example, the fuel plenum wall 63 further defines a plurality of fuel holes 63 a through which fuel is discharged from the fuel plenum 64. As schematically shown in FIGS. 4 and 9 for example, at least one of the fuel holes 63 a is connected in fluid communication with at least one of the fuel jets 61 via the fuel plenum 64. Desirably, each of the fuel holes 63 a is connected in fluid communication with each of the fuel jets 61 via the fuel plenum 64.

As schematically shown in FIGS. 3, 4 and 9 for example, the premixed pilot nozzle 40 further defines a plurality of axially elongated, hollow premix conduits 41 disposed radially outwardly from the fuel plenum wall 63. As schematically shown in the embodiment depicted in FIGS. 4 and 9 for example, each of the premix conduits 41 desirably is defined in part by the plenum wall 63. As schematically shown in FIG. 3 for example, each premix conduit 41 has an upstream end 41 a that is disposed near the downstream end 52 c of the centerbody 52. As schematically shown in FIGS. 4 and 9 for example, each premix conduit 41 defines at its upstream end 41 a an entrance opening 66 a that communicates fluidly with the interior passage 53 of the centerbody 52. The arrows designated 53 a in FIGS. 4 and 9 schematically indicate the flow of air 53 a that enters the entrance opening 66 a of each premix conduit 41 from the interior passage 53 of the centerbody 52.

As schematically shown in FIGS. 4 and 9 for example, each premix conduit 41 is connected in fluid communication with at least one of the fuel holes 63 a that is defined in the fuel plenum wall 63 of the fuel plenum 64. The arrows designated 62 a in FIGS. 4 and 9 schematically indicate the flow of fuel 62 a that exits from the fuel plenum 64 through the fuel holes 63 a defined in the fuel plenum wall 63 and passes into each premix conduit 41. The arrows designated 62 b in FIGS. 4 and 9 schematically indicate the flow of the fuel-air mix 62 b that travels downstream in the premix conduits 41 of the premixed pilot nozzle 40.

As schematically shown in FIGS. 4 and 9 for example, each premix conduit 41 has a downstream end 41 b that is disposed axially opposite the upstream end 41 a of the premix conduit 41 and that is disposed near the downstream end 40 b of the premixed pilot nozzle 40. As schematically shown in FIGS. 4 and 9 for example, each downstream end 41 b of each premix conduit 41 defines an exit opening 66 b that allows fluid, i.e., the fuel-air mix 62 b, to discharge from the hollow premix conduit 41. As schematically shown in FIGS. 4 and 9 for example, each downstream end 41 b of each premix conduit 41 defines a central axis 41 c, and the walls that define each premix conduit 41 are disposed concentrically about this central axis 41 c. Moreover, as schematically shown for the embodiment of the premixed pilot nozzle 40 depicted in FIGS. 4 and 9 for example, each central axis 41 c is a straight line that is disposed so that the flow of the fluid that is the mix of fuel and air that discharges from the exit opening 66 b of each premix conduit 41 is directed parallel to the central axis 36 of the centerbody 52.

While the fuel-air mix 62 b tends to spread radially from each central axis 41 c once the fuel-air mix 62 b leaves the exit opening 66 b of each premix conduit 41, applicants have shown that the radial spread is not very significant. Indeed, applicants' studies have shown that the equivalence ratio at the section of the burn exit plane 44 (FIGS. 4 and 9) that is located immediately downstream of the exit opening 66 b of each premix conduit 41 can be almost twice the equivalence ratio that exists at the section of the burn exit plane 44 (FIGS. 4 and 9) that is located immediately downstream of the central axis 36 of the centerbody 52. High equivalence ratio at a location that is immediately downstream of the exit opening 66 b of each premix conduit 41 can continuously and effectively light the fuel/air mixture through the axially elongating inner cavity 50 c (FIG. 3) and can make the flame stable even if the flame is at lean-blow-out (LBO) condition. This is one of the important roles of a premix pilot, and the premix pilot 60 fulfills this role without an increase of NOx.

Various embodiments of the present invention include features that counteract this much higher equivalence ratio that exists at the section of the burn exit plane 44 (FIGS. 4 and 9) that is located immediately downstream of the exit opening 66 b of each premix conduit 41. As schematically shown for the embodiments of the premixed pilot nozzle 40 that are depicted in FIGS. 3, 4, 5 and 9 for example, the premixed pilot nozzle 40 further defines an annular channel 70 that is disposed radially outwardly from the premix conduits 41. In the embodiments that are depicted in FIGS. 3, 4, 5 and 9 for example, the inner wall 43 of the annular channel 70 also serves to define the outer wall 43 of the premix conduits 41. In the embodiments that are depicted in FIGS. 3, 4, 5 and 9 for example, the centerbody wall 52 a also serves to define the outer wall 52 a of the annular channel 70.

As schematically shown for the embodiments of the premixed pilot nozzle 40 that are depicted in FIGS. 3, 4 and 9 for example, the upstream end of the annular channel 70 is configured to communicate fluidly with the interior passage 53 of the centerbody 52 and thus receives a flow of air from the interior passage 53 of the centerbody 52. At the downstream end of the annular channel 70, a plurality of air jets 42 is defined. At least one of the air jets 42 is disposed nearby at least one of the exit openings 66 b of at least one of the premix conduits 41. Desirably, as shown in FIGS. 4, 5 and 9 for example, at least one of the air jets 42 is disposed nearby each of the exit openings 66 b of each one of the premix conduits 41.

As schematically shown in FIG. 9 for example, each of the passages that defines one of the air jets 42 is defined concentrically around a central axis 42 a that is disposed parallel to the central axis 41 c of the downstream end 41 b of the nearby premix conduit 41. In so doing, the higher velocity air leaving each air jets 42 entrains some of the fuel/air mixture leaving the premix conduits 41 and serves to direct the fuel/air mixture that exists at the section of the burn exit plane 44 (FIG. 9) that is located immediately downstream of the exit opening 66 b of each premix conduit 41. The overall result is a more uniform equivalence ratio at the burn exit plane 44 (FIG. 9) of the fuel-air nozzle 12, and this also can be used by lighting source as a pilot.

As schematically shown in FIG. 4 for example, each of the passages that defines one of the air jets 42 is defined concentrically around a central axis 42 a that is disposed at an acute angle with respect to the central axis 41 c of the downstream end 41 b of the nearby premix conduit 41. The magnitude of this acute angle desirably is in the range of 0.1 degrees to twenty degrees. Moreover, the air jet 42 in the FIG. 4 embodiment desirably is configured and disposed so that the respective air jet 42 directs the flow of air exiting the air jet 42 in a direction away from the nearby one of the exit openings 66 b of the premix conduits 41. Thus, in the embodiment schematically shown in FIG. 4 for example, each air jet 42 is pointed so that the air leaving that air jet 42 moves in a direction that is both downstream and radially away from the central axis 36 of the centerbody 52 as well as radially away from the central axis 41 c of downstream end 41 b of the respective nearby premix conduit 41. In so doing, the air leaving each air jets 42 entrains some of the fuel/air mixture leaving the premix conduits 41 and serves to direct the fuel/air mixture that exists at the section of the burn exit plane 44 (FIG. 4) that is located immediately downstream of the exit opening 66 b of each premix conduit 41 radially outwardly toward the peripheral wall 50 (FIG. 3). The overall result is a more uniform equivalence ratio at the burn exit plane 44 (FIG. 4) of the fuel-air nozzle 12, and this also can be used by lighting source as a pilot.

In another embodiment of the present invention depicted schematically in FIG. 6 for example, with the exception of the embodiment of the premixed pilot nozzle 40 that is depicted schematically in FIG. 6, the embodiment of FIG. 6 is like the embodiment of FIGS. 3, 4, 5 and 9. As schematically in FIG. 6, each of the premix conduits 41 is itself configured concentrically about a central longitudinal axis 41 c that is disposed at an acute angle with respect to the central axis 36 of the centerbody 52. The magnitude of this acute angle desirably is in the range of 0.1 degrees to twenty degrees. Thus, in the premixed pilot nozzle 40 that is depicted schematically in FIG. 6, each of the premix conduits 41 is configured and disposed so as to direct the fuel/air mixture exiting from the exit opening 66 b of each premix conduit 41 radially outwardly away from the central axis 36 of the centerbody 52 so as to form a more uniform fuel/air mixture in the burn exit plane 44 of the fuel-air nozzle 12 and into the combustion chamber of a gas turbine 10 and so as to continuously and effectively light the fuel/air mixture that is supplied through an axially elongating inner cavity 50 c (FIG. 3) of the fuel-air nozzle 12. Though not specifically illustrated in FIG. 6 for example, the axial length of one or more of the premix conduits 41 can extend beyond the downstream end 40 b of the premixed pilot nozzle 40 in a manner concentrically around the central axis 41 c of the downstream end 41 b of premix conduit 41.

In another embodiment of the present invention depicted schematically in FIG. 8 for example, with the exception of the embodiment of the premix conduits 41 of the premixed pilot nozzle 40 that is depicted schematically in FIG. 6, the embodiment of FIG. 8 is like the embodiment of FIGS. 3, 4, 5, 6 and 9. In the embodiment depicted schematically in FIG. 8, each of the premix conduits 41 is itself configured concentrically about a bi-directed central longitudinal axis having a first leg 41 d and a second leg 41 c. As schematically in FIG. 8, the first leg 41 d of the bi-directed central longitudinal axis is disposed parallel to the central axis 36 of the centerbody 52 and extends between the upstream end 41 a and the downstream end 41 b of each premix conduit 41. A second leg 41 c of the bi-directed central longitudinal axis is disposed at an acute angle with respect to the central axis 36 of the centerbody 52 and extends through the downstream end 41 b of each premix conduit 41. The magnitude of this acute angle desirably is in the range of 0.1 degrees to twenty degrees. Thus, the premix conduit 41 that is depicted schematically in FIG. 8 is configured and disposed so as to direct the fuel/air mixture exiting from the exit opening 66 b radially outwardly away from the central axis 36 of the centerbody 52 so as to form a more uniform fuel/air mixture in the burn exit plane 44 of the fuel-air nozzle 12 and into the combustion chamber of a gas turbine 12 and so as to continuously and effectively light the fuel/air mixture that is supplied through an axially elongating inner cavity 50 c (FIG. 3) of the fuel-air nozzle 12.

In another embodiment of the present invention depicted schematically in FIG. 7 for example, with the exception of the embodiment of the premix conduits 41 and annular channel 70 of the premixed pilot nozzle 40 that is depicted schematically in FIGS. 3, 4, 5 and 9, the embodiment of FIG. 7 is like the embodiments of FIGS. 3, 4, 5 and 9. As schematically in FIG. 7, each of the premix conduits 41 is itself configured concentrically about a central longitudinal axis 41 c that is disposed at an acute angle with respect to the central axis 36 of the centerbody 52. The magnitude of this acute angle desirably is in the range of 0.1 degrees to twenty degrees. Thus, in the premixed pilot nozzle 40 that is depicted schematically in FIG. 7, each of the premix conduits 41 is configured and disposed so as to direct the fuel/air mixture exiting from the exit opening 66 b of each premix conduit 41 radially outwardly away from the central axis 36 of the centerbody 52 so as to form a more uniform fuel/air mixture in the burn exit plane 44 of the fuel-air nozzle 12 and into the combustion chamber of a gas turbine 10 and so as to continuously and effectively light the fuel/air mixture that is supplied through an axially elongating inner cavity 50 c (FIG. 3) of the fuel-air nozzle 12.

As schematically shown for the embodiment of the premixed pilot nozzle 40 that is depicted in FIG. 7 for example, the upstream end of the annular channel 70 is configured to taper as it proceeds in the downstream direction toward the air jets 42 that are disposed beside each of the exit openings of premix conduits 41. As described above with regard to the embodiment of FIGS. 3, 4 and 5, each of the air jets 42 is directed radially outwardly from the premix conduits 41 so that each of the air jets 42 can entrain some portion of fuel/air mixture to further direct the mixture radially outwardly from the premix conduits 41 to form a more uniform fuel/air mixture in the burn exit plane 44 of the fuel-air nozzle 12 and into the combustion chamber 32 of a combustor 16 (FIGS. 1 and 2) and to continuously and effectively light the fuel/air mixture that is supplied through an axially elongating inner cavity 50 c (FIG. 3) of the fuel-air nozzle 12.

Each embodiment of the premixed pilot nozzle 40 provides a small well anchored premixed flame near the base of the fuel-air nozzle 12, thus anchoring the swirling fuel air mixture exiting the fuel-air nozzle 12. The improved flame stability enables lower fuel/air operations, thus extending LBO and the emissions operability window.

With fuel/air nozzles 12 such as the embodiments described above, it becomes feasible to implement advantageous methods of operating a fuel/air nozzle 12 for a gas turbine engine 10. One embodiment of such a method of operating a fuel/air nozzle 12 for a gas turbine engine 10 desirably includes the following steps schematically shown in FIG. 10: the step 81 of delivering a primary flow of air 51 a (e.g., FIG. 3) downstream past the swozzle to swirl the primary flow of air; the step 82 of delivering a primary flow of fuel 57 a (e.g., FIG. 3) through the swozzle to mix with the swirled primary flow of air 51 a downstream of the swozzle; the step 83 of delivering a flow of pilot fuel 62 (e.g., FIG. 4) through a hollow fuel supply line 54 to the premix pilot nozzle 40; the step 84 of delivering a secondary flow of air 53 a (e.g., FIG. 4) downstream through the centerbody 52 (e.g., FIG. 3) to the premix pilot nozzle 40; the step 85 of mixing the pilot fuel 62 with the secondary flow of air 53 a in a plurality of axially elongated, hollow premix conduits 41 (e.g., FIG. 4) that discharge the fuel/air mixture 62 b (e.g., FIGS. 4 and 9) from the downstream end 41 b of the premix pilot nozzle 40; and the step 86 of expelling the fuel/air mixture 62 b from the premix conduits 41 of the premixed pilot nozzle 40 away from the central axis 36 of the centerbody 52 (e.g., FIGS. 3, 4 and 6-9).

Another embodiment of such a method of operating a fuel/air nozzle 12 for a gas turbine engine 10 desirably includes the following steps schematically shown in FIG. 11: the step 81 of delivering a primary flow of air 51 a (e.g., FIG. 3) downstream past the swozzle to swirl the primary flow of air; the step 82 of delivering a primary flow of fuel 57 a (e.g., FIG. 3) through the swozzle to mix with the swirled primary flow of air 51 a downstream of the swozzle; the step 83 of delivering a flow of pilot fuel 62 (e.g., FIG. 4) through a hollow fuel supply line 54 to the premix pilot nozzle 40; the step 84 of delivering a secondary flow of air 53 a (e.g., FIG. 4) downstream through the centerbody 52 (e.g., FIG. 3) to the premix pilot nozzle 40; the step 85 of mixing the pilot fuel 62 with the secondary flow of air 53 a in a plurality of axially elongated, hollow premix conduits 41 (e.g., FIG. 4) that discharge the fuel/air mixture 62 b (e.g., FIGS. 4 and 9) from the downstream end 41 b of the premix pilot nozzle 40; the step 87 of diverting some of the secondary flow of air 53 a (e.g., FIGS. 4, 7 and 9) to an annular channel 70 that is disposed radially outwardly from the premix conduits 41 of the premixed pilot nozzle 40; and the step 88 of expelling air from the annular channel 70 away from the premixed pilot nozzle 40 (e.g., FIGS. 4, 7 and 9). Desirably, the pressure of the air expelled from the annular channel 70 exceeds the pressure of the air entering the annular channel 70. Desirably, as schematically shown in FIG. 7 for example, the annular channel 70 includes an upstream end that is configured to taper as it proceeds in the downstream direction. Desirably, as schematically shown in FIG. 7 for example, a further embodiment of the method comprises the step of expelling the fuel/air mixture from the premix conduits 41 of the premixed pilot nozzle 40 away from the central axis 36 of the centerbody 52. Desirably, as schematically shown in FIG. 4 for example, a further embodiment of the method comprises the step of expelling the fuel/air mixture 62 b from the premix conduits 41 of the premixed pilot nozzle 40 in a direction that is parallel to the central axis 36 of the centerbody 52. Desirably, as schematically shown in FIGS. 4 and 7 for example, a further embodiment of the method comprises the step of expelling the fuel/air mixture 62 b from the annular channel 70 in a direction that is radially away from the central axis 36 of the centerbody 52.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A fuel/air nozzle for a gas turbine engine, the fuel/air nozzle comprising: an axially elongating peripheral wall defining an outer envelope of the fuel/air nozzle, the peripheral wall having an outer surface and an inner surface facing opposite the outer surface and defining an axially elongating inner cavity; a hollow, axially elongating centerbody disposed within the inner cavity of the fuel/air nozzle and defining a central axis, the centerbody being defined by a centerbody wall defining an upstream end and a downstream end disposed axially opposite the upstream end, the centerbody wall being defined by an exterior surface and an interior surface facing opposite the exterior surface, the interior surface of the centerbody wall defining an axially elongating interior passage disposed concentrically about the central axis of the centerbody; an elongated, hollow fuel supply line extending axially through the interior passage of the centerbody, the fuel supply line having an upstream end disposed at the upstream end of the centerbody and configured for connection to a source of fuel, the fuel supply line having a downstream end disposed at the downstream end of the centerbody; a primary air flow channel being defined by an annular space between the exterior surface of the centerbody and the inner surface of the peripheral wall; a premixed pilot nozzle having an upstream end connected to the downstream end of the centerbody, the premixed pilot nozzle having a downstream end disposed axially opposite the upstream end of the premixed pilot nozzle; and the premixed pilot nozzle further defining a plurality of axially elongated, hollow premix conduits, each premix conduit having an upstream end disposed near the downstream end of the centerbody and defining an entrance opening that communicates fluidly with the interior passage of the centerbody, each premix conduit having at least one fuel hole being connected in fluid communication with the downstream end of the fuel supply line, each premix conduit having a downstream end defining an exit opening that allows fluid to discharge from the hollow premix conduit, each downstream end of each premix conduit defining a central axis that is not parallel to the central axis of the centerbody.
 2. The fuel/air nozzle as in claim 1, wherein each central axis of at least one premix conduit is disposed at an acute angle with respect to the central axis of the centerbody.
 3. The fuel/air nozzle as in claim 1, wherein the premixed pilot further defines an annular channel disposed radially outwardly from the premix conduits, the annular channel being configured to communicate fluidly with the interior passage of the centerbody, the annular channel defining a plurality of air jets, at least one of the air jets being disposed nearby one of the exit openings of at least one of the premix conduits and having a central axis.
 4. The fuel/air nozzle as in claim 3, wherein the central axis of the upstream end of at least one premix conduit is configured and disposed to extend in a direction parallel to the central axis of the centerbody.
 5. The fuel/air nozzle as in claim 3, wherein the central axis of at least one of the air jets forms an acute angle with the central axis of the centerbody.
 6. The fuel/air nozzle as in claim 3, wherein the annular channel is configured to taper as it proceeds in the downstream direction toward the air jets.
 7. The fuel/air nozzle as in claim 1, further comprising a swozzle including a plurality of swirl blades extending radially across the primary air flow channel, at least one of the swirl blades defining a fuel conduit having an inlet at one end thereof and an outlet at an opposite end thereof in fluid communication with the primary air flow channel.
 8. The fuel/air nozzle as in claim 1, wherein the premixed pilot nozzle defines a pilot fuel nozzle, the pilot fuel nozzle defining an upstream end and a downstream end, the upstream end of the pilot fuel nozzle being connected in fluid communication with the downstream end of the fuel supply line, the downstream end of the pilot fuel nozzle defining at least one fuel jet configured in fluid communication with the upstream end of the pilot fuel nozzle; and the premixed pilot nozzle further defining a fuel plenum wall disposed radially outwardly from the pilot fuel nozzle and defining a fuel plenum between the pilot fuel nozzle and the fuel plenum wall, the fuel plenum wall further defining a plurality of fuel holes, at least one of the fuel holes being connected in fluid communication with at least one of the fuel jets via the fuel plenum, each premix conduit being disposed radially outwardly from the fuel plenum wall and in fluid communication with at least one of the fuel holes.
 9. A combustor for a gas turbine engine, the combustor comprising: a head end portion; at least one fuel/air nozzle carried by the head portion, each fuel/air nozzle further comprising: an axially elongating peripheral wall defining an outer envelope of the fuel/air nozzle, the peripheral wall having an outer surface and an inner surface facing opposite the outer surface and defining an axially elongating inner cavity; a hollow, axially elongating centerbody disposed within the inner cavity of the fuel/air nozzle and defining a central axis, the centerbody being defined by a centerbody wall defining an upstream end and a downstream end disposed axially opposite the upstream end, the centerbody wall being defined by an exterior surface and an interior surface facing opposite the exterior surface, the interior surface of the centerbody wall defining an axially elongating interior passage disposed concentrically about the central axis of the centerbody; an elongated, hollow fuel supply line extending axially through the interior passage of the centerbody, the fuel supply line having an upstream end disposed at the upstream end of the centerbody and configured for connection to a source of fuel, the fuel supply line having a downstream end disposed at the downstream end of the centerbody; a primary air flow channel being defined by an annular space between the exterior surface of the centerbody and the inner surface of the peripheral wall; a premixed pilot nozzle having an upstream end connected to the downstream end of the centerbody, the premixed pilot nozzle having a downstream end disposed axially opposite the upstream end of the premixed pilot nozzle; and the premixed pilot nozzle further defining a plurality of axially elongated, hollow premix conduits, each premix conduit having an upstream end disposed near the downstream end of the centerbody and defining an entrance opening that communicates fluidly with the interior passage of the centerbody, each premix conduit having at least one fuel hole being connected in fluid communication with the downstream end of the fuel supply line, each premix conduit having a downstream end defining an exit opening that allows fluid to discharge from the hollow premix conduit, each downstream end of each premix conduit defining a central axis that is not parallel to the central axis of the centerbody.
 10. The combustor as in claim 9, wherein the premixed pilot further defines an annular channel disposed radially outwardly from the premix conduits, the annular channel being configured to communicate fluidly with the interior passage of the centerbody, the annular channel defining a plurality of air jets.
 11. The combustor as in claim 9, wherein at least one of the air jets is disposed nearby one of the exit openings of at least one of the premix conduits and has a central axis that is disposed at an acute angle with respect to the central axis of the nearby one of the exit openings of at least one of the premix conduits.
 12. The combustor as in claim 9, wherein the annular channel tapers as it proceeds in the downstream direction toward the air jets.
 13. A method of operating a fuel/air nozzle for improved flame stability and NOx in a gas turbine engine, the fuel/air nozzle being defined by a peripheral wall, a hollow centerbody disposed within the peripheral wall and defining a central axis, a swozzle extending from the exterior of the upstream end of the centerbody and radially toward the peripheral wall, and at the downstream end of centerbody a premix pilot nozzle including a plurality of premix conduits having exit openings, the method comprising the steps of: delivering a primary flow of air downstream past the swozzle to swirl the primary flow of air; delivering a primary flow of fuel through the swozzle to mix with the swirled primary flow of air downstream of the swozzle; delivering a flow of pilot fuel through a hollow fuel supply line to the premix pilot nozzle; delivering a secondary flow of air downstream through the centerbody to the premix pilot nozzle; mixing the pilot fuel with the secondary flow of air in a plurality of axially elongated, hollow premix conduits wherein each premix conduit defines a central axis at the downstream end thereof that is not parallel to the central axis of the centerbody and that discharges the fuel/air mixture from the downstream end of the premix pilot nozzle; and expelling the fuel/air mixture from the exit openings of the premix conduits of the premixed pilot nozzle.
 14. The method as in claim 13, further comprising the step of expelling the fuel/air mixture from the premix conduits of the premixed pilot nozzle in a direction that is radially away from the central axis of the centerbody.
 15. The method as in claim 13, further comprising the step of diverting some of the secondary flow of air to an annular channel that is disposed radially outwardly from the premix conduits of the premixed pilot nozzle.
 16. The method as in claim 15, wherein the pressure of the air expelled from the annular channel exceeds the pressure of the air entering the annular channel.
 17. The method as in claim 15, wherein the annular channel tapers as it proceeds in the downstream direction.
 18. The method as in claim 15, further comprising the step of expelling air from the annular channel of the premixed pilot nozzle in a direction that is away from the exit openings of the premix conduits.
 19. The method as in claim 18, wherein the air expelled from the annular channel is directed away from the central axis of the centerbody.
 20. A fuel/air nozzle for a gas turbine engine, the fuel/air nozzle comprising: an axially elongating peripheral wall defining an outer envelope of the fuel/air nozzle, the peripheral wall having an outer surface and an inner surface facing opposite the outer surface and defining an axially elongating inner cavity; a hollow, axially elongating centerbody disposed within the inner cavity of the fuel/air nozzle and defining a central axis, the centerbody being defined by a centerbody wall defining an upstream end and a downstream end disposed axially opposite the upstream end, the centerbody wall being defined by an exterior surface and an interior surface facing opposite the exterior surface, the interior surface of the centerbody wall defining an axially elongating interior passage disposed concentrically about the central axis of the centerbody; an elongated, hollow fuel supply line extending axially through the interior passage of the centerbody, the fuel supply line having an upstream end disposed at the upstream end of the centerbody and configured for connection to a source of fuel, the fuel supply line having a downstream end disposed at the downstream end of the centerbody; a primary air flow channel being defined by an annular space between the exterior surface of the centerbody and the inner surface of the peripheral wall; a premixed pilot nozzle having an upstream end connected to the downstream end of the centerbody, the premixed pilot nozzle having a downstream end disposed axially opposite the upstream end of the premixed pilot nozzle; the premixed pilot nozzle further defining a plurality of axially elongated, hollow premix conduits, each premix conduit having an upstream end disposed near the downstream end of the centerbody and defining an entrance opening that communicates fluidly with the interior passage of the centerbody, each premix conduit defining at least one fuel hole connected in fluid communication with the downstream end of the fuel supply line, each premix conduit having a downstream end defining an exit opening that allows fluid to discharge from the hollow premix conduit, at least each upstream end of each premix conduit defining a central axis configured and disposed so that the flow of fluid that enters the entrance opening of each premix conduit is directed parallel to the central axis of the centerbody; and an annular channel disposed radially outwardly from the premix conduits, the annular channel being configured to communicate fluidly with the interior passage of the centerbody.
 21. The fuel/air nozzle as in claim 20, wherein the upstream end of at least one premix conduit defines a central axis that is not parallel to the central axis of the downstream end of that at least one premix conduit.
 22. The fuel/air nozzle as in claim 20, wherein the annular channel defines a plurality of air jets at a downstream end thereof.
 23. The fuel/air nozzle as in claim 22, wherein at least one of the air jets being disposed nearby one of the exit openings of at least one of the premix conduits and having a central axis that forms an acute angle with the central axis of the centerbody.
 24. The fuel/air nozzle as in claim 23, wherein the central axis of at least one of the air jets directs a flow of air exiting the air jet in a direction away from the central axis of the centerbody.
 25. The fuel/air nozzle as in claim 20, wherein the annular channel is configured to taper as it proceeds in the downstream direction toward the air jets.
 26. A combustor for a gas turbine engine, the combustor comprising: a head end portion; at least one fuel/air nozzle carried by the head portion, each fuel/air nozzle further comprising: an axially elongating peripheral wall defining an outer envelope of the fuel/air nozzle, the peripheral wall having an outer surface and an inner surface facing opposite the outer surface and defining an axially elongating inner cavity; a hollow, axially elongating centerbody disposed within the inner cavity of the fuel/air nozzle and defining a central axis, the centerbody being defined by a centerbody wall defining an upstream end and a downstream end disposed axially opposite the upstream end, the centerbody wall being defined by an exterior surface and an interior surface facing opposite the exterior surface, the interior surface of the centerbody wall defining an axially elongating interior passage disposed concentrically about the central axis of the centerbody; an elongated, hollow fuel supply line extending axially through the interior passage of the centerbody, the fuel supply line having an upstream end disposed at the upstream end of the centerbody and configured for connection to a source of fuel, the fuel supply line having a downstream end disposed at the downstream end of the centerbody; a primary air flow channel being defined by an annular space between the exterior surface of the centerbody and the inner surface of the peripheral wall; a premixed pilot nozzle having an upstream end connected to the downstream end of the centerbody, the premixed pilot nozzle having a downstream end disposed axially opposite the upstream end of the premixed pilot nozzle; and the premixed pilot nozzle further defining a plurality of axially elongated, hollow premix conduits, each premix conduit having an upstream end disposed near the downstream end of the centerbody and defining an entrance opening that communicates fluidly with the interior passage of the centerbody, each premix conduit being connected in fluid communication with the downstream end of the fuel supply line, each premix conduit having a downstream end defining an exit opening that allows fluid to discharge from the hollow premix conduit, each downstream end of each premix conduit defining a central axis configured and disposed so that the flow of fluid that discharges from exit opening is directed parallel to the central axis of each premix conduit; and an annular channel disposed radially outwardly from the premix conduits, the annular channel being configured to communicate fluidly with the interior passage of the centerbody.
 27. The combustor as in claim 26, wherein the annular channel defines a plurality of air jets at a downstream end thereof.
 28. The combustor as in claim 27, wherein at least one of the air jets being disposed nearby one of the exit openings of at least one of the premix conduits and having a central axis that forms an acute angle with the central axis of the centerbody.
 29. The combustor as in claim 28, wherein the central axis of at least one of the air jets directs a flow of air exiting the air jet in a direction away from the central axis of the centerbody.
 30. The combustor as in claim 26, wherein the annular channel is configured to taper as it proceeds in the downstream direction toward the air jets.
 31. A method of operating a fuel/air nozzle for a gas turbine engine, the fuel/air nozzle being defined by a peripheral wall, a hollow centerbody disposed within the peripheral wall and defining a central axis, a swozzle extending from the exterior of the upstream end of the centerbody and radially toward the peripheral wall, and at the downstream end of centerbody a premix pilot nozzle including a plurality of premix conduits having exit openings, the method comprising the steps of: delivering a primary flow of air downstream past the swozzle to swirl the primary flow of air; delivering a primary flow of fuel through the swozzle to mix with the swirled primary flow of air downstream of the swozzle; delivering a flow of pilot fuel through a hollow fuel supply line to the premix pilot nozzle; delivering a secondary flow of air downstream through the centerbody to the premix pilot nozzle; mixing the pilot fuel with the secondary flow of air in a plurality of axially elongated, hollow premix conduits that discharge the fuel/air mixture from the downstream end of the premix pilot nozzle; diverting some of the secondary flow of air to an annular channel that is disposed radially outwardly from the premix conduits of the premixed pilot nozzle; and expelling the fuel/air mixture from the exit openings of the premix conduits of the premixed pilot nozzle.
 32. The method as in claim 31, further comprising the step of expelling the fuel/air mixture from the premix conduits of the premixed pilot nozzle in a direction that is parallel to the central axis of the centerbody.
 33. The method as in claim 31, further comprising the step of expelling the fuel/air mixture from the premix conduits of the premixed pilot nozzle in a direction that is radially away from the central axis of the centerbody.
 34. The method as in claim 31, wherein the pressure of the air expelled from the annular channel exceeds the pressure of the air entering the annular channel.
 35. The method as in claim 31, wherein the annular channel tapers as it proceeds in the downstream direction.
 36. The method as in claim 31, further comprising the step of expelling air from the annular channel of the premixed pilot nozzle in a direction that is away from the exit openings of the premix conduits. 